The present invention relates to a rear-projection screen that receives an image projected from behind on its back surface and displays the projected image on its front surface on the viewing side.
There are rear-projection screens of different types to be disposed in a show window or behind a windowpane to display an image projected thereon by a projector. A known rear-projection screen is formed by applying a diffusing plate, a light interference hologram sheet or a liquid crystal shutter to a glass plate. An image is projected from inside on this rear-projection screen to display the image. Another known rear-projection screen is formed by sandwiching a hologram sheet between transparent glass plates or transparent acrylic resin plates. An image is projected on this rear-projection screen by a projector. These known rear-projection screens are used practically for displaying guidance images, advertisement images and video information. Some known semitransparent screen permits seeing a space behind the semitransparent screen on the side of a projector while images projected on the semitransparent screen by the projector are displayed on the semitransparent screen.
All those known rear-projection screens are incapable of displaying images surpassing the intensity of reflected images and external light reflected from a surface of the screen on the viewing side. Consequently, images, as viewed from the viewing side, have low contrast and are unclear.
A hologram type rear-projection screen, however, places a severe restriction on the range of angle of projection of images by a projector, such as a narrow range about 35xc2x0, and permits the use of only projectors capable of effectively correcting trapezoidal distortion. If vertical viewing angle exceeds 20xc2x0 and horizontal viewing angle exceeds 30xc2x0, chromatic dispersion of the colors of images displayed on the hologram type rear projection screen occurs and makes the images unclear. Moreover, it is very difficult to form a large hologram type rear-projection screen.
Large display screens provided with LED lamps spread all over a display area have been widely used. However, the conventional large display screens are expensive and require troublesome work for installation.
Accordingly, it is an object of the present invention to provide a novel rear-projection screen not reflecting ambient scenery in its surface on the viewing side even in a bright environment, and capable of displaying high-definition images having a high black level and of forming a large screen at a low cost.
According to a first aspect of the present invention, a rear-projection screen comprises: a transparent plate having a rear surface on an image-projecting side, and a front surface on a viewing side; a front transparent sheet applied to the front surface of the transparent plate; and a wide-angle diffusing sheet applied to the rear surface of the transparent plate; wherein the front transparent sheet is provided in its front surface with a plurality of horizontal, parallel, minute ridges having a triangular cross section, a side surface facing up or down of two side surfaces of each minute ridge having a triangular cross section is coated with a shading film, and the other side surface is transparent.
The transparent plate may be a transparent windowpane of a building, the viewing side is on the outer side of the transparent plate, and the image-projecting side is on the inner side of the transparent plate.
The transparent sheet and the wide-angle diffusing sheet may be formed of flexible materials, and surfaces of the transparent sheet and the wide-angle diffusing sheet facing the transparent plate may be adhesive.
According to a second aspect of the present invention, a rear-projection screen comprises: a front transparent sheet having a front surface on a viewing side provided with a plurality of horizontal, parallel, minute ridges each having a triangular cross section, a side surface facing up or down and coated with a shading film and a flat rear surface on an image-projecting side; and a wide-angle diffusing sheet applied to the flat rear surface of the front transparent sheet.
The front transparent sheet and the wide-angle diffusing sheet may be formed of flexible materials, and the rear-projection screen can be rolled in a roll.
The front transparent sheet and the wide-angle diffusing sheet may be formed in a desired plane shape, and may be moved to and installed at an optional position.